Systems and methods for fabricating varying waveguide optical fiber device

Abstract

Systems and methods are described for fabricating a varying-waveguide optical fiber. In one described method, a preform is fabricated having a core and at least one cladding region. The cladding region has a higher viscosity and the core region has a lower viscosity. The relative viscosities of the cladding region and core are chosen such that, when tension is applied to an optical fiber drawn from the preform, the applied tension is primarily borne by the cladding region thereby causing a viscoelastic strain to be frozen into the cladding region, while creating a minimal viscoelastic strain in the core. The method further includes drawing the preform into an optical fiber under an applied tension, such that a viscoelastic strain is frozen into the cladding region the frozen-in viscoelastic strain decreasing the cladding region refractive index. The cladding region refractive index is changed in a section of the optical fiber by heating the section so as to relax the viscoelastic strain frozen into the cladding region in the section of fiber, thereby increasing the cladding region refractive index in the section of fiber.

We claim:  
     
       1. A method for fabricating an optical fiber device, comprising: 
       (a) fabricating a preform including a core and at least one cladding region, the cladding region having a higher viscosity and the core region having a lower viscosity, the relative viscosities of the cladding region and core having been chosen such that, when tension is applied to an optical fiber drawn from the preform, the applied tension is primarily borne by the cladding region, thereby causing a viscoelastic strain to be frozen into the cladding region, while creating a minimal viscoelastic strain in the core;  
       (b) drawing the preform into an optical fiber under an applied tension, such that a viscoelastic strain is frozen into the cladding region, the frozen-in viscoelastic strain decreasing the cladding region refractive index;  
       (c) changing the cladding region refractive index in a section of the optical fiber by heating the section of optical fiber so as to relax the viscoelastic strain frozen into the cladding region in the section of optical fiber, thereby increasing the cladding region refractive index in the section of optical fiber.  
     
     
       2. The method of  claim 1 , wherein step (c) includes applying a controlled amount of heat to the section of optical fiber, the amount of heat being modulated to cause a modulated relaxation of the cladding region in the section of optical fiber, thereby causing a modulated change in the cladding region refractive index in the section of optical fiber. 
     
     
       3. The method of  claim 2 , wherein step (c) further includes: 
       applying modulated amounts of heat along the section of optical fiber so as to cause a modulated relaxation in the frozen-in strain state of the cladding region in the section of optical fiber, thereby causing a modulated increase of the cladding region refractive index in the section of optical fiber.  
     
     
       4. The method of  claim 3 , wherein step (c) further includes: 
       using a stationary heat source that is tailored to produce a heating profile that is designed to cause a modulated relaxation in the frozen-in strain state of the cladding region in the section of optical fiber.  
     
     
       5. The method of  claim 2 , wherein step (c) further includes: 
       applying a controlled amount of heat to the section of optical fiber by scanning a heat source along the section of optical fiber according to a velocity profile so as to cause a modulated relaxation of the frozen-in viscoelastic strain in the cladding region in the section of optical fiber, thereby causing a modulated increase of the cladding region refractive index.  
     
     
       6. The method of  claim 1 , in which the fiber is heated to create three sections: 
       a first section having a first modefield diameter;  
       a second section having a second modefield diameter that is larger than the first modefield diameter; and  
       a transition section between the first section and the second section, the transition section providing an adiabatic transition between the first modefield diameter and the second modefield diameter.  
     
     
       7. The method of  claim 6 , further including: 
       coating the fiber with a polymer having a low refractive index.  
     
     
       8. The method of  claim 1 , wherein the fiber is heated to create three sections: 
       a first section having a refractive index profile matching that of a first fiber design;  
       a second section having a refractive index profile matching that of a second fiber design; and  
       a transition section between the first section and the second section, the transition section providing an adiabatic transition between the first refractive index profile and the second refractive index profile, whereby the device may serve as a low-loss bridge connecting a fiber of the first design with a fiber of the second design.  
     
     
       9. A method for fabricating an optical device, comprising: 
       (a) fabricating an optical fiber including a core and at least one cladding region outside of the core, the cladding region having a higher viscosity and the core having a lower viscosity, the relative viscosities of the cladding region and core having been chosen such that, when tension is applied to the optical fiber, the applied tension is primarily borne by the cladding region, thereby allowing a viscoelastic strain to be frozen into the cladding region, while creating a minimal viscoelastic strain in the core;  
       (b) heating a section of the fiber at or above its strain point while applying a non-zero tension to the region so as to induce a viscoelastic strain state in the cladding region thereby changing the cladding region refractive index;  
       (c) freezing the viscoelastic strain state into the fiber;  
       thus producing a refractive index profile that is modulated along the fiber's length.  
     
     
       10. The method of  claim 9 , wherein the fiber is heated to create three sections: 
       a first section having a first modefield diameter;  
       a second section having a second modefield diameter that is larger than the first modefield diameter;  
       a transition section between the first section and the second section, the transition section providing an adiabatic transition between the first and second modefield diameters.  
     
     
       11. The method of  claim 10 , further including: 
       coating the fiber with a polymer have a low refractive index.  
     
     
       12. The method of  claim 9 , wherein step (b) includes applying along the length of the region a controlled amount of heat that is tailored to cause a modulated change in the viscoelastic strain state of the cladding region in the section of fiber, thereby causing a modulated change in the cladding region refractive index in the section of fiber. 
     
     
       13. The method of  claim 9 , wherein the fiber is heated to create three sections: 
       a first section having a refractive index profile matching that of a first fiber design;  
       a second section having a refractive index profile matching that of a second fiber design; and  
       a transition region between the first region and the second region, the transition region providing an adiabatic transition between the first refractive index profile and the second refractive index profile, whereby the device may serve as a low-loss bridge connecting a fiber of the first design with a fiber of the second design.  
     
     
       14. A method for fabricating an optical device, comprising: 
       (a) fabricating an optical fiber including a core and at least one cladding region, the cladding region having a higher viscosity and the core having a lower viscosity, the relative viscosities of the cladding and core regions having been chosen such that, when tension is applied to the optical fiber, the applied tension is primarily borne by the cladding region thereby allowing a viscoelastic strain to be frozen into the cladding region, while creating a minimal viscoelastic strain in the core;  
       (b) heating a section of the fiber to a temperature that is at or near the fiber's strain point; and  
       (c) applying a controlled tension to the fiber, the applied tension being modulated so as to freeze a modulated strain state into the glass, thereby creating a modulated cladding region refractive index profile.  
     
     
       15. The method of  claim 14 , wherein step (b) includes applying a controlled amount of heat to the region, the amount of heat being modulated along the length of the section of fiber. 
     
     
       16. The method of  claim 15 , wherein the heat source is moved relative to the fiber according to a velocity profile that is modulated along the length of the section of fiber. 
     
     
       17. The method of  claim 14 , in which the fiber is heated to create three sections: 
       a first section having a first modefield diameter;  
       a second section having a second modefield diameter that is larger that the first modefield diameter;  
       and a transition section between the first section and the second section, the transition section providing an adiabatic transition between the first and second frozen-in strain states.  
     
     
       18. The method of  claim 17 , further including: 
       coating the fiber with a polymer having a low refractive index.  
     
     
       19. The method of  claim 14 , wherein the fiber is heated to create three sections: 
       a first section having a refractive index profile matching that of a first fiber design;  
       a second section having a refractive index profile matching that of a second fiber design; and  
       a transition section between the first section and the second section, the transition section providing an adiabatic transition between the first refractive index profile and the second refractive index profile, whereby the device may serve as a low-loss bridge connecting a fiber of the first design with a fiber of the second design.  
     
     
       20. A method for fabricating an optical fiber device, comprising: 
       (a) fabricating a preform including a core and at least one cladding region, the cladding region having a higher viscosity and the core region having a lower viscosity, the relative viscosities of the cladding and core regions having been chosen such that, when tension is applied to an optical fiber drawn from the preform, the applied tension is primarily borne by the cladding region, thereby causing a viscoelastic strain to be frozen into the cladding region, while creating a minimal viscoelastic strain in the core;  
       (b) drawing the preform into an optical fiber under an applied tension, such that a viscoelastic strain is frozen into the cladding region, the frozen-in viscoelastic strain decreasing the cladding region refractive index; and  
       (c) modifying the fiber's photosensitivity in a section of the fiber by heating the section so as to relax the viscoelastic strain frozen into the cladding region in the section of fiber.  
     
     
       21. An optical fiber device, comprising: 
       an optical fiber having a core and at least one cladding region, the cladding region having a higher viscosity and the core region having a lower viscosity, the relative viscosities of the cladding region and core having been chosen such that a desired viscoelastic strain state may be frozen into, or relaxed out of, the cladding region, creating a minimal change in the viscoelastic strain state of the core,  
       the cladding region having a viscoelastic strain state that has been modulated to produce a modulated refractive index along a length of the cladding region.  
     
     
       22. The optical fiber device of  claim 21 , wherein the viscoelastic strain state of the cladding region has been modulated to create three sections in the optical fiber: 
       a first section having a refractive index profile matching that of a first fiber design;  
       a second section having a refractive index profile matching that of a second fiber design; and  
       a transition section between the first section and the second section, the transition section providing an adiabatic transition between the first refractive index profile and the second refractive index profile, whereby the device may serve as a low-loss bridge connecting a fiber of the first design with a fiber of the second design.  
     
     
       23. The optical fiber device of  claim 21 , in which the fiber is heated to create three sections: 
       a first section having a first modefield diameter;  
       a second section having a second modefield diameter that is larger than the first modefield diameter; and  
       a transition section between the first section and the second section, the transition section providing an adiabatic transition between the first modefield diameter and the second modefield diameter.  
     
     
       24. A system for fabricating an optical fiber device, comprising: 
       at least one fiber guide for holding an optical fiber to be processed;  
       a heat source for applying a controlled amount of heat to a section of the optical fiber;  
       a tensioning assembly for applying a controlled tension to the optical fiber;  
       a measurement device for monitoring optical properties of the optical fiber as it is processed; and  
       a controller for controlling the amount of heat and applied tension based upon the optical properties monitored by the measurement device, the controller using the controlled heat and applied tension to modulate the optical fiber's viscoelastic strain state.